Pressure actuated jarring device for use in a wellbore

ABSTRACT

A pressure actuated jarring apparatus includes a tubular housing, a piston, a spring element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The piston is disposed within the central bore and is movable axially between an inactivated state and an activated state. The spring element is configured to store energy to drive the piston from the activated state. The seat is coupled to the piston such that when a plug is seated in an orifice of the seat fluid is prevented from flowing through the orifice. The jarring device is fired by increasing pressure in the passage until the plug is forced through the seat, thereby releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 62/480,135, filed Mar. 31, 2017, the entirety of which is incorporated herein by reference.

BACKGROUND

During the drilling, work over, or plug and abandonment of oil and gas producing wellbores, a variety of downhole tools may be attached to a pipe (often referred as a drillstring) or coiled tubing string and utilized to perform various functions within the wellbore. Occasionally, these downhole tools become lodged or stuck in the wellbore. When this situation occurs, a fishing assembly can be deployed in the wellbore to attempt to free or dislodge the stuck object. In general, fishing assemblies employ a jarring or impact device that can deliver repeated blows to the stuck tool in an operation that is referred to as a “fish”.

SUMMARY

Embodiments described herein are directed to a pressure actuated jarring apparatus for use in a wellbore. According to an embodiment, a jarring apparatus comprises a tubular housing, a piston, a spring element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The piston is disposed within the passage of the tubular housing and is movable axially within the passage between an inactivated state and an activated state. The spring element is disposed within the tubular housing to store energy to drive the piston from the activated state. The seat is coupled to the piston and has an orifice, such that when a plug is seated in the seat the orifice is blocked and fluid is prevented from flowing through the orifice. When the orifice is blocked and the piston is in the activated state, the pressure actuated jarring device is fired by increasing pressure in the passage until the plug is forced through the seat, thereby opening the orifice, releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.

Embodiments described herein are also directed to a pressure actuated jarring apparatus comprising a tubular housing, an upper piston, a lower piston, a compressible element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The upper piston is disposed within the passage of the tubular housing and is movable axially within the passage between an inactivated state and an activated state. The upper piston has one or more ports through a sidewall of the upper piston. The lower piston is coupled to the upper piston and has a top face and an elongation. An annular cavity is formed between the elongation and the tubular housing and the annular cavity at least partially filled with a compressible fluid. The spring element is disposed within the annular cavity to store energy to drive the upper piston and the lower piston from the activated state. The seat is coupled to the upper piston or the lower piston and has an orifice, such that when a plug is seated in the seat, the orifice is blocked and fluid is prevented from flowing through the orifice. When the orifice is blocked and the first and lower pistons are in the activated state, the pressure actuated jarring device is fired by increasing pressure in the passage until the plug is forced through the orifice, thereby opening the orifice, releasing the energy in the spring element and driving the first and lower pistons from the activated state so that the upper piston impacts an abutment and generates a jarring force.

Embodiments described herein are also directed to a method of generating a jarring force to free a stuck object in a wellbore. The method comprises deploying a plug through a coiled tubing or workstring until the plug engages a seat of a jarring apparatus and blocks flow through an orifice of the seat. The method also includes pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move a piston of the jarring apparatus from an inactivated state to an activated state against a force imparted on the piston by a spring element. The method also includes increasing the pressure of the fluid to force the plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the embodiments described herein will be more fully disclosed in the following detailed description, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:

FIG. 1 is a side cross-sectional view of a pressure actuated jarring apparatus in an inactivated state, according to an embodiment.

FIG. 2 is a side cross-sectional view of the pressure actuated jarring apparatus of FIG. 1 in an activated state, according to an embodiment.

FIG. 3 is a side cross-sectional view of the lower piston of a pressure actuated jarring apparatus, according to one embodiment.

FIG. 4 is a side cross-sectional view of a seat, according to an embodiment, in a first position with a plug engaged with the seat.

FIG. 5 is a side cross-sectional view of the seat of FIG. 4 in a second configuration.

FIG. 6 is a side cross-sectional view of a piston with two seats, according to an embodiment.

FIG. 7 is an elevation view of the pressure actuated jarring apparatus of FIG. 1 deployed in a wellbore.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship.

Objects, such as tools, can often become stuck in a wellbore. When this situation occurs, a fishing assembly that is coupled to coiled tubing, a workstring, or drillstring in the wellbore can be used to attempt to dislodge the object. In general, a fishing assembly includes a jarring device that, when fired, delivers an upward impact or jarring force to dislodge the stuck object. Two common types of jarring devices are known. The first type is a hydraulic jar that operates based on tension or compression. The second type of jarring device is fluid actuated.

To deliver an upward impact with a hydraulic jarring device, the drillstring or coiled tubing first provides a downward force for a given period of time to “cock” the jarring device. A tensile force is then applied and held for some period of time, generally about 1½ to 2 minutes, until the jarring device fires (i.e., delivers an impact or jarring force). However, because the drillstring or coiled tubing applies both compressive and tensile forces for each jarring cycle, fatigue results, particularly in the coiled tubing. Consequently, only a limited number of impacts can be delivered before the coiled tubing string must be exited from the wellbore so that the fatigued length of coil can be removed. Exiting the wellbore not only is time consuming, but the removal of the length of coiled tubing then places any future fatigue-inducing stresses into a different location on the coiled tubing string. Moreover, further time is consumed by the wait time that is required between impacts. If many impacts are needed to dislodge the object, the amount of time to dislodge a stuck object can be substantial.

Hydraulic jarring device also typically do not function well (or at all) in horizontal well applications due to the inability to set down enough weight to cock the jarring device. This inability is caused by the frictional forces between the drillstring and the wellbore. The weight transfer from the drillstring to the jarring device diminishes as the length of the horizontal portion of the well increases.

Known fluid actuated jarring devices likewise can have disadvantages. For example, many such devices again require the application of tensile or compressive forces to actuate the tool. The amount of tensile or compressive forces must correlate precisely with the fluid flowrate that is applied. If the amount of tension is too great, the fishing assembly will stall. If the amount of tension is too little, the jarring device will not produce impacts. Therefore, fluid actuated jarring devices can present challenges with their successful operation.

Moreover, many fluid actuated jarring devices do not have the ability to transmit torque through the tool, which is an attribute often required in fishing operations. Yet further, the magnitude of the impacts delivered by many fluid actuated jarring devices can be limited. The magnitude of the impact is a function of momentum, which, by definition, is the mathematical product of velocity and the mass of the moving object (which in this case is an anvil (e.g., a piston)). Generally, the velocity is provided via a compression spring having a known spring force. However, the spring force is limited by the physical dimensions and properties of available springs and the tool itself. The mass of the anvil is a function of its physical dimensions and the density of the material from which it is made. In general, fluid actuated jarring devices offer no means to increase the impact force beyond that delivered by the spring nor any means of increasing the mass of the anvil.

Accordingly, embodiments described herein are directed to a pressure actuated jarring apparatus that is part of a fishing assembly that is deployed in a wellbore to dislodge a stuck object or tool. The pressure actuated jarring apparatus can be coupled to coiled tubing and deployed in the wellbore when an object becomes stuck, or it can be utilized in daily downhole operations, such as drilling or other types of remedial work, as a preventative measure in the event that a drillstring or workstring does become stuck in the wellbore. In embodiments described herein, when not being used in a fishing operation, fluid can flow unobstructed through a central passageway of the jarring apparatus. When a fishing operation is initiated, the jarring apparatus is operated by restricting fluid flow through the jarring apparatus, such as by dropping a ball or other plugging device to obstruct the fluid passageway. Restriction of the fluid flow causes one or more pistons to shift from an inactivated state to an activated state in which a compressive element (e.g., a spring) stores potential energy. The fluid pressure applied to the plug can then be increased until the plug is dislodged, at which point the potential energy is released and the jarring device is fired. When fired, the released energy drives the one or more pistons from the cocked position and into contact with an abutment. The impact between the piston and the abutment creates a jarring force that helps to dislodge the stuck object.

In one embodiment, as shown in FIGS. 1, 2 and 7, a pressure actuated jarring apparatus 5 that is part of a fishing assembly includes a top sub 20, a bottom sub 25, a tubular housing 30 (made up of portions 30 a, 30 b), a piston 40 (made up of pistons 40 a, 40 b), a seat 50, and a spring element 60. The apparatus 5 is configured for engagement to a workstring or coiled tubing (“WS,” shown in FIG. 7) on its upper end 10 and to a fishing or latching tool (“F,” shown in FIG. 7) on its lower end 15. The top sub 20 can be coupled to the workstring WS in any appropriate manner. In the embodiment shown in FIGS. 1, 2 and 7, the top sub 20 contains a thread 22 for engagement to the workstring WS. Similarly, the bottom sub 25 can be coupled to the fishing or latching tool F in any appropriate manner. In the embodiment shown in FIGS. 1 and 2, the bottom sub 25 includes a thread 27 for engagement to the fishing or latching tool F.

As can be seen in FIGS. 1 and 2, the top sub 20 defines a central bore 200 and the bottom sub 25 defines a central bore 230. The tubular housing 30 extends from an upper end 31 to a lower end 32 and defines a passage 34 between the upper end 31 and the lower end 32. The upper end 31 is configured to couple to the top sub 20 and the lower end 32 is configured to couple to the bottom sub 25. The tubular housing 30 can be coupled to the top sub 20 in any appropriate manner, such as via a threaded connection 65. The tubular housing 30 can be coupled to the bottom sub 25 in any appropriate manner, such as via a threaded connection 80.

In embodiments, the tubular housing 30 can be manufactured as two independent housings for ease of machining, such as an upper tubular housing 30 a and a lower tubular housing 30 b (referred to collectively as tubular housing 30). The upper tubular housing 30 a and the lower tubular housing 30 b can be joined in any appropriate manner, such as via a threaded connection 70.

The piston 40 is disposed within the passage 34 of the tubular housing 30 and is movable axially within the passage 34 between an inactivated state (shown in FIG. 1) and an activated state (shown in FIG. 2). The piston 40 can be constructed of any appropriate material. For example, in one embodiment, the piston 40 is constructed of a material having a density higher than that of steel, such as tungsten (which has a density approximately 2½ times that of steel), to maximize its mass and, thereby, increase the jarring force created by the jarring apparatus 5 when it is fired.

The piston 40 can include an upper piston 40 a and a lower piston 40 b (referred to collectively as piston 40). The upper piston 40 a and the lower piston 40 b are coupled such that they move together from the inactivated state to the activated state. The pistons 40 a, 40 b can be coupled using any appropriate method. For example, in an embodiment, the upper piston 40 a and the lower piston 40 b are connected via threaded engagement 75. Although the illustrated embodiment uses an upper piston 40 a and a lower piston 40 b, any number of pistons can be used, including one piston, three pistons, four pistons, five pistons, or more. The addition of pistons increases the overall mass of the piston assembly and thus increases the jarring force generated by the apparatus 5 when it is fired.

The upper piston 40 a defines a central bore 210 and the lower piston 40 b defines a central bore 220. The upper piston 40 a contains a seal element 85 and the lower piston 40 b contains a seal element 95. The seal elements 85, 95 create a seal between the piston 40 and the tubular housing 30. Further, tubular housing 30 can include a seal element 90 configured to engage the outside of the piston 40. As a result, fluid is blocked from flowing around the outside of the pistons 40 a, 40 b so that fluid flow is directed instead through the pressure actuated jarring apparatus 5 via the central bores 200, 210, 220, and 230. The seal elements can be elastomeric elements, such as, for example, o-rings. The lower piston 40 b can also include a retainer 55 for retaining the lower piston 40 b with respect to the bottom sub 25 and to retain the spring element 60 during assembly. For example, the retainer 55 can be a snap ring.

In an embodiment, the upper piston 40 a includes port(s) 105 through a shaft 42 of the upper piston 40 a. Fluid is allowed to pass through the port(s) 105 into a cavity 110 formed between the upper piston 40 a, the lower piston 40 b, and the tubular housing 30. As a result, the fluid is able to exert pressure on multiple portions of the piston 40. Hence, by providing the port(s) 105, the addition of pistons increases the force applied to the spring element 60 for a given amount of fluid pressure, thereby increasing the potential energy of the jarring apparatus 5 when in the activated state.

The piston 40 includes an external shoulder 130 and the tubular housing 30 includes an internal shoulder 135. As shown in FIG. 2, when the piston 40 is in the activated state, the external shoulder 130 contacts the internal shoulder 135. This contact limits the travel of the upper piston 40. The positions of the external shoulder 130 and the internal shoulder 135 can be configured to limit the travel of the piston 40 at the desired location when in the activated state to provide the desired jarring force.

The spring element 60 is disposed within the passage 34 of the tubular housing 30 and is configured to store energy to drive the piston 40 from the activated state toward the inactivated state. The upper end of the spring element 60 is in contact with the piston 40 and the lower end of the spring element 60 is in contact with the bottom sub 25. The spring element may comprise any of a variety of resilient materials, such as a compression spring(s), Belleville washers, elastomeric springs, and/or compressible fluid. The spring element also can comprise a combination of materials. For example, a compressible fluid can be used in conjunction with, for example, a compression spring.

In one embodiment, a sealed annulus 44 is formed between the piston 40, the tubular housing 30, and the bottom sub 25. The sealed annulus 44 can be, at least partially, filled with a compressible fluid to increase the force applied on the piston 40 when in the activated state. This compressible fluid is used as a fluid compression spring to maximize piston velocities during the jarring procedure. The combination of a physical spring, such as a compression spring, with a fluid spring exerts a large upward force on the piston 40. These features, in combination with the high density of the piston 40, create a jarring device capable of delivering high magnitude impacts.

The seat 50 is coupled to the piston 40. The seat 50 has an orifice 122 aligned with the central bore of the piston 40. The orifice 122 has a diameter that is less than the diameter of the central bore of the piston 40. Hence, the seat 50 is configured to receive a plug in the orifice 122 such that the plug blocks fluid from passing through the central bore 220 of the lower piston 40 b and/or the central bore 210 of the upper piston 40 a when the apparatus 5 is in the activated state. The plug can engage a shoulder 125 of the seat 50. In an embodiment, the seat 50 and the piston 40 are manufactured as a single component. Alternatively, the seat 50 can be joined to the piston 40 through any appropriate means including welding, bonding, thread engagement, and press-fit. The piston 40 can include a seal element 100 configured to engage the seat 50 to prevent fluid from flowing around the seat 50.

The plug 120 can be any appropriate object that can block the flow of fluid through the orifice. For example, the plug can be a spherical ball commonly used in the downhole drilling industry. In one embodiment, the seat 50 is intended for use with a deformable ball.

In other embodiments, the seat is expandable from a first configuration to a second configuration so that it can be used with non-deformable plugs, such as plugs made of steel. For example, the seat 50 can be made of a deformable material. In another embodiment, an expandable seat 160 is used. In one example, as shown in FIGS. 4 and 5, the expandable seat 160 includes one or more splits or grooves 165 that allow the expandable seat 160 to flex. FIG. 4 shows an expandable seat 160 in a first configuration with a plug 120 engaged with a shoulder 180 of the seat 160. With the plug 120 in this position, fluid is prevented from flowing through the expandable seat 160. The expandable seat 160 is maintained in this position by a biasing member 150 disposed between the expandable seat 160 and the piston 40. The expandable seat 160 is able to move axially within a piston bore 175 formed in the piston 40, from a first position to a second position. In the first configuration, as shown in FIG. 4, the seat 160 is substantially restricted within the bore 175 and is held in place via the biasing member 150. As pressure increases, the seat travels downward to a second position in which the seat is disposed in an enlarged bore 170. In this position, the seat 160 can expand to the second configuration and the plug 120 is allowed to travel through the seat 160, as illustrated in FIG. 5. The pressure actuated jarring apparatus 5 fires precisely at the moment the plug 120 travels through the seat 160, creating an upward impact and pressure pulse. The seat 160 can include a seal element 155 configured to engage the piston 40 to prevent fluid from flowing around the seat 160.

FIG. 6 illustrates lower piston 40 b comprising two seats 50. The two seats 50 can be manufactured as one piece. Alternatively, the two seats 50 can be separate components. Pressure actuated jarring apparatus 5 can be configured to operate with any number of seats 50, which can be made of various materials, and have any configuration of orifice 122 sizes. These seats 50 can be configured in any appropriate manner suitable for the operating pressures in the particular application in which the jarring apparatus 5 is employed.

In operation, the operator can use the pressure actuated jarring apparatus 5 to dislodge a tool that is stuck in a wellbore. The operator can select an appropriate plug 120 to provide a desired jarring impact. The plug 120 can then be pumped from the surface through the workstring until it engages the seat 50, 160. Optionally, the operator can apply a tensile load to the fishing assembly via the toolstring or workstring. Fluid pressure in the central bore can then be slowly increased until the pressure required to force the plug 120 to pass through the seat 50 is achieved, at which point the pressure actuated jarring apparatus 5 fires. The piston 40 is driven upward until the piston 40 impacts an abutment 145 within the jarring apparatus. In the embodiment shown, the abutment 145 is the bottom face of the top sub 20 (shown in FIG. 2). In another embodiment, the abutment is provided by an internal stop, shoulder or abutment in the central bore of the tubular housing 30. In the embodiment shown, the upper face 140 of the upper piston 40 a is configured to contact the abutment 145. In other embodiments, a flange or shoulder of the upper piston 40 a or the lower piston 40 b is configured to contact the abutment 145. The mechanical impact between the piston 40 and the abutment 145 creates a jarring force. In addition, when the jarring apparatus 5 is coupled to coiled tubing, the release of pressure that occurs when the plug passes through the seat can result in a pressure pulse that causes the coiled tubing to spring upward and, thus, further enhance the jarring force that is created. If the stuck object does not come free, this process can be repeated.

The amount of stroke of the piston 40 and the resulting impact forces is partially dictated by the spring constant, or stiffness, of the spring element(s) 60 used. The magnitude of the impact is also dictated by the amount of pressure that is needed to force the plug 120 through the seat 50. This force is based on the size and material of the plug 120. Generally, as the plug diameter or size increases, so does the amount of force needed to drive the plug 120 through the seat 50. The material from which the plug 120 is constructed also can affect the force required for the plug 120 to pass through the seat 50. Providing a range of plugs 120 of various sizes and/or physical properties allows an operator to fire the pressure actuated jarring apparatus 5 at a range of pressures. For example, the operator can begin firing the pressure actuated jarring apparatus 5 at a low pressure then slowly increase the pressure until the stuck object is free.

As shown in FIG. 3, the lower piston 40 b can include a cavity 182. After the plug 120 passes through the seat 50, 160, the plug 120 may be captured in the cavity 182. In another embodiment, the plug 120 may be captured in an additional sub (not shown) below the jarring apparatus 5. The lower piston 40 b may contain drain holes 185 to allow fluid to exit the cavity 182.

FIG. 7 illustrates the pressure actuated jarring apparatus 5 attached to a workstring WS inside a wellbore WB and attached to a latching or fishing tool F. A shock sub (not shown) can be attached above the pressure actuated jarring apparatus 5. The shock sub allows the fishing assembly to travel upwards with each impact of jarring apparatus 5 without having to move the entire workstring, which could be several thousand feet long. A shock sub thus can allow for the stuck object to be more easily dislodged and removed from the wellbore.

In another embodiment, a method of generating a jarring force to free a stuck object in a wellbore is provided. The method includes pumping a plug 120 through a coiled tubing or workstring until the plug 120 engages a seat 50, 160 of a jarring apparatus and blocks flow through an orifice 122, 162 of the seat 50, 160. The method also includes pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move a piston 40 of the jarring apparatus from an inactivated state to an activated state against a force imparted on the piston 40 by a spring element 60. The method also includes increasing the pressure of the fluid to force the plug 120 through the orifice 122, 162 of the seat 50, 160, thereby releasing the pressure on the piston 40 and allowing the piston 40 to be moved by the spring element 60 toward the inactivated state.

The method can also include pumping a second plug 120 through the coiled tubing or workstring until the second plug engages the seat 50, 160 of the jarring apparatus and blocks flow through the orifice 122, 162 of the seat 50, 160, wherein the second plug has a larger diameter than the first plug. The method can also include pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move the piston 40 of the jarring apparatus from the inactivated state toward the activated state against a force imparted on the piston 40 by the spring element 60. The method can also include increasing the pressure of the fluid to force the second plug through the orifice 122, 162 of the seat 50, 160, thereby releasing the pressure on the piston 40 and allowing the piston 40 to be moved by the spring element 60 toward the inactivated state.

Although the devices, kits, systems, and methods have been described in terms of exemplary embodiments, they are not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the devices, kits, systems, and methods, which may be made by those skilled in the art without departing from the scope and range of equivalents of the devices, kits, systems, and methods. 

What is claimed is:
 1. A pressure actuated jarring apparatus for use in a wellbore, comprising: a tubular housing having a passage therethrough extending from an upper end to a lower end; a piston disposed within the passage of the tubular housing and movable axially within the passage between an inactivated state and an activated state; a spring element disposed within the tubular housing to store energy to drive the piston from the activated state; and a seat coupled to the piston and having an orifice, such that when a plug is seated in the seat the orifice is blocked and fluid is prevented from flowing through the orifice, wherein, when the orifice is blocked and the piston is in the activated state, the pressure actuated jarring apparatus is fired by increasing fluid pressure in the passage until the plug is forced through the seat, thereby opening the orifice, releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.
 2. The pressure actuated jarring apparatus of claim 1, wherein the tubular housing includes an upper tubular housing and a lower tubular housing.
 3. The pressure actuated jarring apparatus of claim 1, wherein the piston includes an upper piston and a lower piston disposed within the tubular housing and movable axially within the passage between the inactivated state and the activated state.
 4. The pressure actuated jarring apparatus of claim 3, wherein the upper piston includes one or more ports through a shaft of the upper piston configured to allow fluid traveling through the pressure actuated jarring apparatus to pass through the one or more ports and into a cavity formed between the shaft of the upper piston, the tubular housing, and a top face of the lower piston.
 5. The pressure actuated jarring apparatus of claim 1, wherein a sealed annulus is formed between the piston and the tubular housing and the spring element is disposed within the sealed annulus and wherein the sealed annulus is at least partially filled with a compressible fluid.
 6. The pressure actuated jarring apparatus of claim 1, wherein the piston defines a cavity configured to receive and retain the plug after the plug passes through the orifice of the seat.
 7. The pressure actuated jarring apparatus of claim 1, wherein the orifice of the seat is expandable from a first configuration to a second configuration, and wherein the plug is unable to pass through the orifice when in the first configuration and is able to pass through the orifice when in the second configuration.
 8. The pressure actuated jarring apparatus of claim 7, wherein the seat is axially movable relative to the piston from a first position to a second position, and wherein the orifice is restricted from expanding when the seat is in the first position and is able to expand when the seat is in the second position.
 9. The pressure actuated jarring apparatus of claim 8, further comprising a biasing member disposed between the seat and the piston, the biasing member configured to bias the seat toward the first position.
 10. The pressure actuated jarring apparatus of claim 1, further comprising a second seat.
 11. A pressure actuated jarring apparatus for use in a wellbore, comprising: a tubular housing having a passage therethrough extending from an upper end to a lower end, wherein the upper end is configured to couple to a workstring or coiled tubing sub and the lower end is configured to couple to a fishing tool; an upper piston disposed within the passage of the tubular housing and movable axially within the passage between an inactivated state and an activated state, the upper piston having one or more ports through a sidewall of the upper piston; a lower piston coupled to the upper piston, the lower piston having a top face and an elongation, wherein an annular cavity is formed between the elongation and the tubular housing, the annular cavity at least partially filled with a compressible fluid; a compressible element disposed within the annular cavity to store energy to drive the upper piston and the lower piston from the activated state; and a seat coupled to the upper piston or the lower piston and having an orifice, such that when a plug is seated in the seat, the orifice is blocked and fluid is prevented from flowing through the orifice, wherein, when the orifice is blocked and the first and lower pistons are in the activated state, the pressure actuated jarring apparatus is fired by increasing pressure in the passage until the plug is forced through the orifice, thereby opening the central bore, releasing the energy in the compressible element and driving the first and lower pistons from the activated state so that the upper piston impacts an abutment and generates a jarring force.
 12. The pressure actuated jarring apparatus of claim 1, wherein the tubular housing includes an upper tubular housing and a lower tubular housing.
 13. The pressure actuated jarring apparatus of claim 11, wherein the lower piston defines a cavity configured to receive and retain the plug after the plug passes through the orifice of the seat.
 14. The pressure actuated jarring apparatus of claim 11, wherein the orifice of the seat is expandable from a first configuration to a second configuration, and wherein the plug is unable to pass through the orifice when in the first configuration and is able to pass through the orifice when in the second configuration.
 15. The pressure actuated jarring apparatus of claim 14, wherein the seat is axially movable relative to the first and lower pistons from a first position to a second position, and wherein the orifice is restricted from expanding when in the first position and is able to expend when in the second position.
 16. The pressure actuated jarring apparatus of claim 15, further comprising a biasing member disposed between the seat and the lower piston, the biasing member configured to bias the seat toward the first position.
 17. A method of generating a jarring force to free a stuck object in a wellbore, comprising: deploying a first plug through a coiled tubing or workstring until the first plug engages a seat of a jarring apparatus and blocks flow through an orifice of the seat; pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move a piston of the jarring apparatus from an inactivated state to an activated state against a force imparted on the piston by a spring element; and increasing the pressure of the fluid to force the first plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state.
 18. The method of claim 17, further comprising: deploying a second plug through the coiled tubing or workstring until the second plug engages the seat of the jarring apparatus and blocks flow through the orifice of the seat, wherein the second plug has a larger diameter than the first plug; pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move the piston of the jarring apparatus from the inactivated state to the activated state against a force imparted on the piston by the spring element; and increasing the pressure of the fluid to force the second plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state. 